Excessive exposure of human skin to either the rays of the sun or to sun lamps which emit ultraviolet radiation similar to natural sunlight can result in sunburn or erythema solars as the condition is medically defined.
In order to substantially reduce or prevent sunburn, various sunscreen compositions have been proposed which contain sunscreen agents which scatter the sunlight, or which absorb the ultraviolet portion of the sun's radiant energy, i.e., energy radiation equivalent to about 2800 to about 4000 angstrom units.
For topical application, sunscreen compositions must be non-toxic and non-irritating to the skin, and capable of application to the skin as a uniform continuous film. In addition, the active sunscreening agents in the sunscreen compositions must be chemically stable. In particular, the sunscreening agents must be resistant to chemical and photodegradation when on the skin, as well as resistant to absorption through the skin.
A wide variety of sunscreen preparations are available. Sunscreens which have both functional and aesthetic characteristics, however, are nevertheless sought. Typically, the sunscreen preparations of the art have been chemically-based compositions that employ synthetic materials such as para-aminobenzoic acid (PABA) derivatives as the sunscreen agent. Although the chemically-based sunscreen compositions of the art have been effective in reducing sunburn, many users suffer allergic reactions to these products. Also, uncertainty exists over the effects of long term exposure of the skin to chemically-based sunscreen compositions.
A need therefore exists for sunscreen formulations that employ a minimum of synthetic chemical ingredients but yet provide effective protection against ultraviolet light absorption.